1. Field of the Invention
The present invention relates generally to sealing gaskets used for pipe joints in which a male spigot pipe section is installed within a mating female socket pipe section.
2. Description of the Prior Art
Pipes formed from thermoplastic materials including polyethylene polypropylene and PVC are used in a variety of industries. In forming a joint between sections of pipe, the spigot or male pipe end is inserted within the female or socket pipe end. An annular, elastomeric ring or gasket is typically seated within a grove formed in the socket end of the thermoplastic pipe. As the spigot is inserted within the socket, the gasket provides the major seal capacity for the joint. It is critical, during the installation process, that the gasket not be able to twist or flip since a displaced or dislocated gasket will adversely affect the ultimate sealing capacity of the joint.
Irrespective of the type of sealing action of the sealing element, such as compression sealing action, lip sealing action or a combination thereof, it is necessary that the sealing gasket consists of a relatively soft elastomeric material. However, a sealing ring which is formed entirely of a material which is sufficiently soft and elastomeric to provide the sealing function has the disadvantage that it is difficult to retain in the desired position in a groove in connection with the joining of sections of pipe. There is also the risk that such a sealing ring will be displaced from its sealing position in the pipe joint if the difference of the internal or external pressures on either side of the sealing ring are sufficiently great.
In the early 1970's, a new technology was developed by Rieber & Son of Bergen, Norway, referred to in the industry as the "Rieber Joint." The Rieber system employed a combined mould element and sealing ring for sealing a joint between the socket end and spigot end of two cooperating pipes formed from thermoplastic materials. In the Rieber process, the elastomeric gasket was installed within a simultaneously formed internal groove in the socket end of the female pipe during the pipe belling process. The provision of a prestressed and anchored elastomeric gasket during the belling process at the pipe factory provided an improved socket end for a pipe joint with a sealing gasket which would not twist or flip or otherwise allow impurities to enter the sealing zones of the joint, thus increasing the reliability of the joint and decreasing the risk of leaks or possible failure due to abrasion. The Rieber process is described in the following issued United States patents, among others: U.S. Pat. Nos. 4,120,521; 4,061,459; 4,030,872; 3,965,715; 3,929,958; 3,887,992; 3,884,612; and 3,776,682.
It should be evident that a sealing ring of the type under consideration could be made entirely of elastically yielding material, such as rubber. Such a design would be simple and could be produced relatively easily with uncomplicated production equipment. However, as has been discussed, such sealing rings made entirely of elastically yielding material generally lack the necessary support effect to avoid being dislodged during field installation procedures and may not be suitable for use as a combined mould element, as described above.
The groove provided in the female or socket pipe end may assume various shapes. The problem of retaining the sealing rings during joining of pipes is even more important in the case where the female groove has a bottom surface which is at least partly rounded in shape. In these cases, axially directed forces can create substantial twisting within the seal ring. In order to address the above problems, different approaches have been suggested to compensate for the lack of support effect in sealing rings made of elastically yielding material. The previously mentioned U.S. Pat. No. 3,776,682 uses a separate support member to support the mould element when producing the socket end of the pipe. However, the construction is more or less unsupported as a sealing ring. U.S. Pat. No. 3,500,047 shows a design utilizing two mould element support rings connected to the sealing ring. A design featuring three separate parts complicates the manufacturing operation, however.
In other designs, the sealing ring, in addition to the elastically yieldable material, includes either an internal or external retainer ring or band which is intended to support the gasket during the manufacturing operation and/or during field installation procedures and transport.
In those designs utilizing external reinforcing bands or rings, it is possible that water, sewage waste or other contaminates could corrode metal surfaces, thereby compromising the integrity of the pipe joint.
It is an object of the present invention to provide a sealing gasket of elastically yielding material which is suitable for use as a combined mould element and sealing ring while providing a reinforced region which is entirely embedded within the elastically yielding material.
Another object of the invention is to provide a sealing gasket with an embedded steel band of unique shape which allows the band to be thinner in cross-section than previous designs.
Another object of the invention is to provide a sealing gasket with an embedded metal band which features improved adhesion of the metal to the rubber of the gasket.
Another object of the invention is to provide such a gasket with an embedded band which avoids metal to water contact in use.
Another object of the invention is to provide such a gasket design with an embedded metal band of a unique configuration which avoids metal to water contact while at the same time provides a reinforced contact point for reinforcing the gasket during the combined moulding operations.